Plastic forming of hollow bodies has heretofore encompassed a wide variety of processes and techniques including but not limited to blow molding, stretch-blow molding, thermoforming and the like. For example, hollow bodies having threaded necks are produced from injection-molded preforms which are heated and then expanded by high pressure air through a process called blow molding. At times the preform is allowed to cool down prior to arrival at the blow molding station from the injection molding station and then it must be thermally conditioned within a relatively narrow tolerance to a temperature that is suitable for a subsequent stretching process. In order to obtain uniform and good orientation, the temperature variation across the wall of the body should be within 10 degrees Celsius and not much above 10 degrees Celsius from the glass transition temperature of the plastic to be stretch-blown during the forming process. The closer the temperature is to the glass transition temperature, the more orientation is obtained. However, much higher pressure is required to stretch and blow the container at the lower temperature; therefor, a compromise has to be made. The oriented hollow bodies thus obtained exhibit a mechanical strength which is markedly improved to the point that the bodies can generally be used for packaging carbonated beverages under pressure. The air pressure used in this known process for stretch-blow molding can exceed 1,000 pounds per square inch (psi) if a particular bottom design is required for such containers. Other features, such as molded-in impressions, horizontal rings to resist buckling of the container, and vertical lines to improve stackability all require even higher air pressure during the forming process.
Heat-setting of polyethylene terephthalate (PET) bottles, or other shapes of containers, by stretch-blowing the preforms in a high temperature mold is presently used to crystallize the PET. This process is complicated and requires long cycle times. The container is first heated and then cooled by the mold. Therefore, the larger the change in temperature, in order to speed the crystallization, the more energy is consumed during the process, and compromises must be made between the energy use and the speed of the process.
Also, it is known in the prior art that the containers, such as plastic bottles used for beverages, and containers for food products and the like for human or animal consumption, need to be sterilized to avoid contamination of the food, beverages and the like. Heretofore, this sterilization process required an additional process step following completion of the container forming and following the step of exhausting the pressurized air used during the blow molding process.
Another shortcoming of the prior art is that during the extrusion of the plastic material and the shaping of the preform, formation of actealdehydes, or ethanol, occurs. These products are toxic in nature and can remain in the container body following the use of pressurized air during the blow molding process.